1. Technical Field of the Invention
The present invention relates to a method of detecting an end point of chemical-mechanical polishing (CMP) of a wafer, and further to an apparatus for detecting an end point of polishing of a wafer with which the method is embodied, in which a permalloy magnetic layer or a metal layer for a device is formed on a surface of a substrate made of silicon, an alumina-titanium carbide alloy, LCD glass, an electric circuit made of Cu, Ag or Au is provided if necessary, and the wafer on which an insulating layer has been formed is chemimechanically polished.
2. Description of the Related Art
The CMP has been developed for providing smooth topographies on surfaces deposited on semiconductor substrates.
A method of CMP has been employed as follows. A wafer xe2x80x9cwxe2x80x9d is bonded to a plate of a holder with wax so as to be pressed against a platen to which a polishing cloth has been bonded. While supplying polishing-material slurry to the platen, the platen and the wafer are rotated to polish an insulating layer or metal layer by chemimechanically polishing the wafer until the permalloy layer or the metal layer for a device is exposed to the outside.
Another method has been employed as follows. A wafer is vacuum-adsorbed to a chuck table, and then a platen to which a polishing cloth has been bonded on the plate of a head is pressed from the upper surface of the wafer. While supplying polishing-material slurry to the upper surface of the wafer, the platen and the wafer are rotated to polish the insulating layer or metal layer by the chemimechanically polishing (CMP) the wafer until the permalloy layer or the metal layer for a device is exposed to the outside.
In the CMP process, the overall surface of the permalloy layer or the metal layer for a device is coated with copper, aluminum, silver or gold. Then, an excess portion of the metal is chemimechanically polished to obtain a device wafer having an electric circuit made of copper, aluminum, silver or gold. In another CMP process, the overall surface of the permalloy layer or the metal layer is coated with an insulating layer made of silicon oxide, aluminum oxide or titanium oxide. Then, an excess portion of the insulating layer is chemimechanically polished so that a flat wafer is obtained in which the insulating layer is mixed with the device. FIG. 10 shows a multilayer circuit structure formed on a silicon wafer xe2x80x9cwxe2x80x9d having a MOSFET (refer to Japanese Patent Laid-Open No. 10-303152 and GB2324750A). On a surface of a silicon oxide insulating layer 101a of a polished silicon substrate 101, the multilayer circuit includes: (1) a tungsten (W) contact plug portion 102 for connecting the MOSFET to an upper-layer circuit; (2) an aluminum local circuit portion 103 for establishing the electric connection in the CMOS circuit block; and (3) a copper global circuit portion 104 in which copper is embedded in an organic film having a low dielectric constant.
The device isolation among the MOSFET of the foregoing device wafer is performed by a CMP method to be a flattening device isolating structure in which the silicon oxide films are embedded in grooves formed in the silicon substrate 101. Then, a BPSG film 105 is grown on the MOSFET, and then the BPSG film is flattened by the CMP method. Then, a diffusion layer of the MOSFET and a contact hole which reaches the gate electrode are provided for the flattened BPSG film 105. Polishing-material slurry prepared by dispersing silica colloidal particles in oxidizer solution and the CMP method are used to form the W contact hole plug. A first embedded aluminum circuit in which aluminum is embedded in the first circuit groove formed in the first silicon oxide film 106 is formed on the W contact hole plug. Moreover, a second embedded aluminum circuit is formed by embedding aluminum in a first through hole and a second circuit groove, which are formed in the second silicon oxide film 107 formed above the first embedded aluminum circuit.
The foregoing embedded aluminum circuits are formed in such a manner that aluminum embedded films are formed in the circuit groove and the through holes by a high-temperature sputtering method, and the Al-CMP method with the polishing-material slurry are employed to flatten the surface.
Moreover, a second through hole is formed in an organic film 108 formed on the second siliconoxide film 107 and having a low dielectric constant; a third embedded copper circuit is formed by embedding copper in a third circuit groove; a third through hole is formed; and a fourth embedded copper circuit is formed by embedding copper in a fourth circuit groove. The foregoing embedded copper circuits are formed by embedding copper in the circuit grooves and/or through holes to form copper films by an MOCVD method. Then, the polishing-material slurry is used to perform a CMP polishing operation so as to flatten the surface.
To manufacture the device wafer having the MOSFET, the metal embedding and flattening process using W, Al, Cu, Ti, TiN, WSix, TiSix and the like is frequently employed in a metal CMP method. Also isolation and formation of the flattened device and flattening of the surface of the BPSG film are performed by the oxide-film CMP method.
As shown in FIGS. 11A to 11D, the magnetic head substrate is processed such that a wafer 1 (see FIG. 11A) having a substrate 101 on which a permalloy layer 109 is formed. Then, an aluminum insulating layer 110 is furthermore formed. The wafer 1 is polished by the CMP method until the permalloy layer is exposed to the outside (see FIG. 11D) by chemimechanically polishing the wafer 1. As a result, a plurality of the permalloy layers, for example, two to five permalloy layers are sometimes formed.
An automatic (unmanned) polishing means for polishing the wafer has been required from a market. Thus, a variety of CMP automatic polishing apparatuses for automatically detecting an end point of polishing have been suggested. The end point of polishing is detected by any one of the following methods.
(1) The thickness of the wafer which is being polished is measured by a thickness meter to determine the end point in accordance with an amount of polishing (refer to Japanese Patent Laid-Open No. 62-257742, Japanese Patent Laid-Open No. 9-193003, Japanese Patent Laid-Open No. 10-106984 and Japanese Patent Laid-Open No. 10-98016).
(2) A method for determine the end point in accordance with a load electric current, voltage or change in the resistance of the motor of the platen or the chucking mechanism which is performing the polishing operation (refer to Japanese Patent Laid-Open No. 61-188702, Japanese Patent Laid-Open No. 6-252112, Japanese Patent Laid-Open No. 8-99625, Japanese Patent Laid-Open No. 9-70753, Japanese Patent Laid-Open No. 10-44035, Japanese Patent Laid-Open No. 10-128658 and Japanese Patent Laid-Open No. 10-177976).
(3) A method of determining the end point of polishing in accordance with change in the torque of the motor of the platen or the chucking mechanism which is performing the polishing operation (refer to Japanese Patent Laid-Open No. 5-138529, Japanese Patent Laid-Open No. 6-216095, Japanese Patent Laid-Open No. 8-139060, Japanese Patent Laid-Open No. 8-197417, Japanese Patent Laid-Open No. 9-36073, Japanese Patent Laid-Open No. 9-262743 and Japanese Patent Laid-Open No. 10-256209).
(4) A method in which the wafer being polished is irradiated with a laser beam to determine the end point of polishing in accordance with the quantity of reflected light (refer to Japanese Patent Laid-Open No. 57-138575, Japanese Patent Laid-Open No. 61-214970, Japanese Patent Laid-Open No. 4-255218, Japanese Patent Laid-Open No. 5-309559, Japanese Patent Laid-Open No. 7-328916, Japanese Patent Laid-Open No. 8-174411, Japanese Patent Laid-Open No. 9-7985 and Japanese Patent Laid-Open No. 10-160420).
(5) A method in which phosphorus or tracer particles serving as an index is added to the polishing-material slurry to measure the quantity of the index on the polishing cloth so as to determine the end point of polishing (refer to Japanese Patent Laid-Open No. 2-241017 and Japanese Patent Laid-Open No. 8-69987).
A method in which a differential interference microscope is used to observe the surface of the wafer to determine the end point of polishing (refer to Japanese Patent Laid-Open No. 5-234971 and Japanese Patent Laid-Open No. 5-226203).
The method (1) in which the thickness of the wafer is measured is arranged such that the thickness of only a part of the wafer is measured. Since a long time is required to measure the distribution of thicknesses of the overall portion of the wafer, only a poor accuracy can be realized.
Each of the determining method (2) in which the electric current, the voltage or the resistance is used and the method (3) in which the torque is used, is not a method of directly observing the surface of the polished wafer. Also only a poor accuracy of flattening can be obtained.
The method (4) in which the quantity of reflected laser beam is used, is arranged such that the wafer is directly irradiated with the laser beam to determine the end point in accordance with the quantity of reflected light. Therefore, presence of water of the polishing-material slurry for use in the CMP polishing process on the surface of the wafer causes data to be scattered. Hence it follows that an apparatus for cleaning and drying the position on the surface of the wafer on which the laser beam is made incident and from which the same is reflected must be joined. Therefore, the foregoing method cannot be employed when the size of the CMP apparatus is reduced. What is worse, the cost of the apparatus cannot be reduced. Moreover, the polishing process is interrupted because the cleaning and drying processes of the wafer have to be performed.
The method (5) in which the index is added cannot be employed because influences on polishing of the wafer and on a post-process performed after the CMP polishing process has been completed are not known.
An object of the present invention is to provide a method of detecting an end point of polishing of a wafer and an apparatus for detecting an end point using the foregoing method, which are free from deflection of detected data concerning the physical properties of the surface of the wafer, even if water is present on the surface of a wafer or if the process for flattening the surface of the polished wafer is being performed and, therefore, the distance from the detecting apparatus to the wafer has a slight deviation.
According to a first aspect of the present invention, there is provided a method of detecting an end point of polishing of a wafer, comprising the steps of: using a color identifying sensor for recognizing a color component of light by applying light from a light source and by converging reflected light to an optical fiber to cause the color identifying sensor to previously recognize a color component of a substance of a wafer which must be polished; displaying an ON-state when the color component is recognized and an OFF-state when the color component is not recognized; one point (except for the central point) of the surface of the rotating wafer is irradiated with light emitted from the color identifying sensor to cause the color identifying sensor to detect the number of times (m) of off-states at predetermined intervals of time during an operation for polishing the wafer; and determining an end of polishing of the wafer when the detected number of times (m) coincides with the number (n) of off-states indicating an optimum end point of polishing of the wafer in a predetermined time which has previously been recorded.
According to a second aspect of the present invention, there is provided a method of detecting an end point of polishing of a wafer, comprising the steps of: using a color identifying sensor for recognizing a color component of light by applying light from a light source and by converging reflected light to an optical fiber to cause the color identifying sensor to previously recognize a color component of a substance of a wafer which must be polished; displaying an ON-state when the color component is recognized and an OFF-state when the color component is not recognized; one point (except for the central point) of the surface of the rotating wafer is irradiated with light emitted from the color identifying sensor to digital-display, on an axis of abscissa, on- and off-time at predetermined time during an operation for polishing the wafer; causing an integrated value (xcexa3m) of digital-displayed off-pulse widths in a predetermined time to be detected; and determining an end of polishing of the wafer when the detected integrated value (xcexa3m) coincides with an integrated value (xcexa3n) of off-pulse widths indicating a previously recorded optimum end point of polishing of the wafer in a predetermined time.
According to a third aspect of the present invention, there is provided a method of detecting an end point of polishing of a wafer, comprising the steps of: using a color identifying sensor for recognizing a color component of light by applying light from a light source and by converging reflected light to an optical fiber to cause the color identifying sensor to previously recognize a color component of a substance of a wafer which must be polished; displaying an ON-state when the color component is recognized and an OFF-state when the color component is not recognized; one point (except for the central point) of the surface of the rotating wafer is irradiated with light emitted from the color identifying sensor to cause the color identifying sensor to detect the number of times (m) of off-states at predetermined intervals of time during an operation for polishing the wafer; and determining an end of polishing of the wafer when the detected number of times (m) coincides with the number (n) of off-states indicating an optimum end point of polishing of the wafer in a predetermined time which has previously been recorded and when a detected integrated value (xcexa3m) coincides with an integrated value (xcexa3n) of off-pulse widths indicating a previously recorded optimum end point of polishing of the wafer in a predetermined time after performing the steps of digital-displaying, on an axis of abscissa, on- and off-time at predetermined time during an operation for polishing the wafer and causing an integrated value (xcexa3m) of digital-displayed off-pulse widths in a predetermined time to be detected.
According to a fourth aspect of the present invention, there is provided a method of detecting an end point of polishing of a wafer, wherein the wafer, which must be polished, is a wafer having a device provided for the surface of a silicon substrate thereof, and the overall surface of the wafer is coated with copper.
According to a fifth aspect of the present invention, there is provided a method of detecting an end point of polishing of a wafer according, wherein the predetermined time is time required to rotate the wafer one time.
According to a sixth aspect of the present invention, there is provided an apparatus for detecting an end point of polishing of a wafer arranged to be provided for an apparatus for chemimechanically polishing a wafer, the apparatus for detecting an end point of polishing of a wafer, comprising:
(a) a color identifying sensor arranged to recognize a color component of light by applying light from a light source, converge reflected light to an optical fiber and previously recognize a color component of a substance of a wafer which must be polished and capable of displaying an ON-state when the color component is recognized and an OFF-state when the color component is not recognized;
(b) a counter mechanism for irradiating one point (except for the central point) of the surface of the rotating wafer with light emitted from the color identifying sensor to detect the number of times (m) of off-states at predetermined intervals of time during an operation for polishing the wafer;
(c) a storage mechanism for storing the number of detection times;
(d) a calculating mechanism for making a comparison between the number of times (m) of off-states communicated from the counter mechanism as a signal and the number (n) of off-states previously recorded in the storage mechanism and indicating an optimum end point of polishing of the wafer in a predetermined time; and
(e) a control mechanism for transmitting, to a chemimechanical polishing apparatus, a signal indicating a fact that a moment of time at which m=n is an end point of polishing of the wafer.
According to a seventh aspect of the present invention, there is provided an apparatus for detecting an end point of polishing of a wafer arranged to be provided for an apparatus for chemimechanically polishing a wafer, the apparatus for detecting an end point of polishing of a wafer, comprising:
(a) a color identifying sensor arranged to recognize a color component of light by applying light from a light source, converge reflected light to an optical fiber and previously recognize a color component of a substance of a wafer which must be polished and capable of displaying an ON-state when the color component is recognized and an OFF-state when the color component is not recognized;
(b) a counter mechanism for irradiating one point (except for the central point) of the surface of the rotating wafer with light emitted from the color identifying sensor to digital-display, on an axis of abscissa, on- and off-time at predetermined time during an operation for polishing the wafer so as to detect an integrated value (xcexa3m) of digital-displayed off-pulse widths in a predetermined time;
(c) a mechanism for storing the detected integrated value;
(d) a calculating mechanism for making a comparison between the detected integrated value (xcexa3m) and an integrated value (xcexa3n) of off-pulse widths indicating a previously recorded optimum end point of polishing of the wafer in a predetermined time; and
(e) a control mechanism for transmitting, to a chemimechanical polishing apparatus, a signal indicating a fact that a moment of time at which xcexa3m=xcexa3n is an end point of polishing of the wafer.
According to an eighth aspect of the present invention, there is provided a CMP apparatus for chemimechanically polishing a wafer including a plurality of layers having an insulating layer and a metal layer on the insulating layer, the CMP apparatus comprising:
a chuck plate for holding the wafer;
a platen facing to the chuck plate; and
a color identifying sensor having a light source emitting light to a polished surface of the wafer and an optical fiber converging the light reflected on the polished surface of the wafer, the color identifying sensor for recognizing a color component of the light.
According to a ninth aspect of the present invention, there is provided the CMP apparatus according to the eighth aspect of the present invention, wherein the color identifying sensor previously recognizes a color component of a substance of the wafer.
According to a tenth aspect of the present invention, there is provided the CMP apparatus according to the ninth aspect of the present invention, wherein the color identifying sensor displays an ON-state when the color component is recognized and an OFF-state when the color component is not recognized.
According to an eleventh aspect of the present invention, there is provided the CMP apparatus according to the eighth aspect of the present invention, wherein the color identifying sensor having a detecting unit for emitting the light generated from the light source through the optical fiber, converging the light reflected on the wafer.
According to the twelfth aspect of the present invention, there is provided the CMP apparatus according to the eight aspect of the present invention, wherein the detecting unit of the color identifying sensor faces to the wafer disposed on the chuck plate.
In the present invention, a color identifying sensor is used which is capable of obtaining data about a detected color component of light of metal in the surface of the metal of the surface of the wafer or the insulating film which is free from deviation even if water is present on the surface of a wafer or if the process for flattening the surface of the polished wafer is being performed. Therefore, detection of an end point of polishing of the wafer can accurately be performed.